Per i2c-mux-pca954x.yaml, the I2C subnodes should follow the
'i2c@' format.
Change it to fix the following schema warning:
imx8mm-nitrogen-r2.dtb: i2c-mux@70: Unevaluated properties are not allowed ('i2c3@0' was unexpected)
	from schema $id: http://devicetree.org/schemas/i2c/i2c-mux-pca954x.yaml#
Signed-off-by: Fabio Estevam <festevam@denx.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>
                #address-cells = <1>;
                #size-cells = <0>;
 
-               i2c3@0 {
+               i2c@0 {
                        reg = <0>;
                        #address-cells = <1>;
                        #size-cells = <0>;